I don't regret going to art school; I learned a lot of valuable stuff in a much shorter span of time compared to if I was self-taught. I liked having the opportunity to learn new approaches to drawing from different instructors and building up a network of art peers.
BUT-- I would never advise anyone go to a for-profit art school today. I started college in '08, and it was expensive then-- but by the time I graduated in 2013, it was STUPID expensive-- and the prices only go up every year. I consider myself fortunate that I graduated with under 50k in debt, while these days it seems impossible to get a degree for less than 80-100k. @_@ Is an art degree worth that much? Absolutely not. No way.
Still, I don't 100% agree with people who say "You don't need school, you can learn everything on the internet!" That might work for some, but there are artists who strongly benefit from having the kind of structure and mentorship that a classroom (physical or virtual) provides. That doesn't make them stupid or lazy, and I think we can agree that different learning methods work for different people. That said, there are many more affordable alternatives to expensive private schools, inlcuding online mentorships and classes that come at a fraction of the cost.
Also, it's totally reasonable to be upset with your instructors if they're crap at their job. You're paying for a service with the expectation of having a knowledgeable instructor-- it would be really weird to willingly pay for poor instruction. If I go to a restaurant and they serve me really shitty food I don't shrug and go "Oh well, that's life! I'll just cook something myself :u" It's not the teacher's job to make you do the work and achieve a specific skill level, but it is their job to at least know what they're talking about and offer you guidance.